This invention relates to an electric circuit interrupter of the vacuum type and, more particularly, to a circuit interrupter of this type which comprises two sets of relatively movable contacts electrically connected in parallel for carrying continuous current through the interrupter.
In most vacuum interrupters, the force required to hold a pair of separable contacts in engagement during the passage of high current therethrough varies directly with the square of the current. It has been recognized that this force can be reduced by providing a plurality of sets of contacts electrically connected in parallel for sharing the total current through the interrupter. One way of constructing such an interrupter is to mount the movable contact of each pair on the usual long, slender movable contact rod and to arrange these movable contact rods in close side-by-side relationship. A problem involved in such an arrangement is that the high magnetic forces developed between the movable contact rods when high currents flow therethrough tend to force the rods together, making it difficult to properly guide and operate the contact rods.
One solution to this problem is disclosed and claimed in co-pending application Ser. No. 579,122 -Kurtz and Sofianek, filed May 19, 1975, now Pat No. 3,996,438, and assigned to the assignee of the present invention. In that application, the two electrically-parallel pairs of contacts are located at opposite ends of the envelope of the interrupter, and current is carried physically past each contact pair via an electrically-parallel conductive path extending through the other pair. Each of these parallel conductive paths is constituted, in part, by a single one of the rod electrodes of a rod-array type of electrode arrangement of the general type disclosed and claimed in U.S. Pat. No. 3,679,474 -Rich, assigned to the assignee of the present invention. On the distal end of this single rod electrode, means is provided for mounting the stationary contact of the pair of relatively movable contacts in the parallel path.
A problem involved in such a design is that high magnetic forces of attraction can be developed between the movable contact rod and the parallel single rod electrode in the region where these parts are in proximity. In the aforesaid Kurtz and Sofianek application, this problem is solved by providing around each movable contact rod a conductive tube that is electrically connected in series with the aforesaid single rod electrode. This tube distributes the current flowing through the single rod electrode circumferentially about the movable contact rod surrounded by the tube, thereby providing a coaxial conductor arrangement wherein relatively low forces are present between the conductors.